Inventions relating to cleaning of stack gases from any fossil fuel source, such as those from coal-fired power plants, from natural or propane burning heating plants, or from cement kilns, were disclosed in Ser. No. 15/067,569 and its ancestor applications. The stack gases exhausted from such facilities are controlled by environmental regulations. Such regulations require abatement of carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxide (NOx), sulfur oxide (SOx) as well as halogens (such as chloride and fluorides) and trace metals, particularly mercury, lead, and zinc. The present application discloses and claims flow-through solid catalysts formed by coating the zeolite material on a metal or ceramic solid substrate. In some embodiments, the solid substrate is formed as flat plates, corrugated plates, or honeycomb blocks.
Various methods and apparatuses have been proposed for abating these pollutants in stack gases. In particular, a variety of methods have been proposed for reducing pollutants released from coal-fired stack gas. One method of cleaning coal-fired stack gas is the use of scrubbers that inject a liquid or slurry into a gas stream that washes various pollutants, such as with acidic compounds, from the stack gas stream. Another type of cleaning is the use of an exhaust burner that combusts volatile materials and other combustible compounds reducing pollution in the stack gas.
Specifically, it has been proposed that the stack gases be mixed with ammonia or urea and then passed through a catalyst in which the ammonia or urea reacts selectively with the nitrous oxides to form nitrogen gas in water vapor, or combustion of a sulfur-containing fossil fuel in the presence of a calcium carbonate or magnesium carbonate to form calcium sulfate or magnesium sulfate. See U.S. Pat. Nos. 8,181,451; 6,706,246; 5,525,317; 5,237,939; 4,185,080; and 4,051,225. It has also been proposed to reduce nitrogen in stack gas by passing the stack gas through a heat exchange having a SCR catalyst. See U.S. Pat. No. 5,918,555. Reduction of sulfur oxide content in stack gases has been proposed involving catalyzed oxidation to sulfur trioxide in the presence of an absorbent or combusting sulfur-containing fuel in a combustion zone charged with a slurry in sulfuric acid solution. See U.S. Pat. Nos. 5,540,755; 4,649,034; 4,284,015; and 4,185,080. Catalytically converting unburned hydrocarbons and carbon monoxide to carbon dioxide and reducing nitrogen oxides to nitrogen subsequent to the combustion of fossil fuels, while absorbing sulfur oxide has been proposed, where the catalytic material is physically combined into a dry powder of an adsorbent matrix selected from calcium aluminate, calcium aluminate cement, barium titanate, and calcium titanate. See U.S. Pat. No. 4,483,259. It has also been proposed to pass the stack gases through a solid catalyst of a combination of active metals on the surface that is capable of reducing or converting sulfur oxides, carbon monoxide and hydrocarbons to inert compounds such as carbon dioxide, water and nitrogen. See U.S. Pat. No. 7,399,458. Levels of mercury in stack gases from coal combustion have also been reduced by introducing a sorbent composition into the gas stream in a zone where temperature is greater than 500° C., where the sorbent composition comprises an effective amount of nitrate salt and/or a nitrite salt. See U.S. Pat. Nos. 7,468,170 and 7,731,781.
Other types of cleaning stack gas have also been proposed and will be known to those having skill in the art. These previous proposals have a number of drawbacks. Many require addition of another gas or liquid such as ammonia, sulfuric acid, or the presence of an active metal catalyst.
One particular problem unresolved by current technology is carbon gaseous pollutants that cannot be reduced by scrubbing or combustion. It has been proposed to capture the carbon in the form of carbon dioxide, compress the carbon dioxide, and store it in a geological formation. Zeolite has been proposed among other materials to absorb carbon dioxide, and after sequestering the carbon dioxide then to be able to regenerate the zeolite material. See “Carbon Dioxide Capture Using a Zeolite Molecular Sieve Sampling System for Isotopic Studies (13C and 14C) of Respiration”, Radiocarbon, 47, 441-451 (2005); “Absorbent Materials for Carbon Dioxide Capture from Large Anthropogenic Point Sources”, ChemSusChem 2009, 2, 796-854; “NIST Provides Octagonal Window of Opportunity for Carbon Capture”, NIST Techbeat, Feb. 7, 2012. These uses of zeolite generally involved large particle sizes of zeolite; for example, between 1/16 and ⅛ inch in size under conditions to provide for adsorption of carbon dioxide and later regeneration. These methods of absorbing carbon dioxide highlight the continuing problem of disposing of sequestered carbon dioxide.
There is therefore still a need for a method and apparatus to effectively remove carbon monoxide, carbon dioxide, nitrogen oxides, sulfur oxides and trace metals, such as mercury, from stack gases without consuming expensive catalysts, without injecting additional gases, liquids and/or solids into the stack gas, and without creating waste products that themselves present problems and costs in disposal. This is of particular concern in cleaning of stack gases from coal power plants because of the release of volatiles such as coal tar and other active pollutants along with carbon dioxide in the stack gas.
An added compounding problem is the water vapor content of the stack gas reaching the cleaning system. The moisture content of typical stack gas exited from a baghouse and directed to a stack gas cleaning system is typically 12% to 14% water, or more, and the difficulty of stack gas cleaning with the available water vapor content causes the catalyst to be swamped and inoperative for commercial applications. The catalyst is inoperative to reduce carbon monoxide, carbon dioxide, nitrogen oxides and sulfur oxides to produce oxygen and residuals. Therefore there is still a need for an effective and commercially viable method of reducing the water vapor content of stack gas before reaching the catalyst so that the catalyst can effectively reduce carbon monoxide, carbon dioxide, nitrous oxides and sulfur oxides to oxygen and residuals.
Presently disclosed is an apparatus for drying and cleaning stack gases comprising: (a) a first flow-through solid catalyst of natural calcium zeolite with a porosity of a total surface area of not greater than 1200 m2/g adapted to reduce carbon oxides present in an exhaust stack; (b) a second flow-through solid catalyst of a blend of natural sodium zeolite and natural calcium zeolite of a porosity with a total surface area of not greater than 1200 m2/g adapted to reduce sulfur oxides present in the exhaust stack downstream of the first solid catalyst; (c) a third flow-through solid catalyst of natural calcium zeolite with a porosity of a total surface area not greater than 1200 m2/g adapted to reduce nitrogen oxides present in the exhaust stack downstream of the second solid catalyst; (d) a pair of electrodes adapted to be positioned inline in the gas flow upstream of the first flow-through solid catalyst and insulated from containment of the gas flow, such as a pipe, and applying D.C. voltage between the electrodes to ionize water vapor without creating substantial amounts of hydrogen gas and reduce moisture content of the gas flow through the flow-through solid catalyst; (d) an exhaust stack adapted to provide a gas flow, selected from the group consisting of volatiles from combustion of coal or from combustion of natural gas or from a cement kiln, sequentially past the pair of electrodes and through the first flow-through solid catalyst, the second flow-through solid catalyst, and the third flow-through solid catalyst, each solid catalyst collecting residuals, and providing stack gases exiting the third flow-through solid catalyst with at least 70% reduction in sulfur oxides, nitrogen oxides, and carbon oxides; and (e) optionally the first flow-through solid catalyst, the flow-through solid catalyst, and the third flow-through solid catalyst each adapted to be periodically purged with nitrogen to remove solids and/or liquids collected in the first flow-through solid catalyst, the second flow-through solid catalyst, and/or the third flow-through solid catalyst so each flow-through solid catalyst can be prepared for reuse. Note the first flow-through solid catalyst, the second flow-through solid catalyst, and the third flow-through solid catalyst may include other zeolites particle sizes as explained in more detail below.
Here as elsewhere in this application “flow-through solid catalyst” means a substrate on which the described zeolite solid catalyst is applied to enable a desired gas stream to flow through. The substrate may be a plate type, honeycomb or corrugated as described in more detail below, although the plate type is preferred. The substrate is metal (e.g. stainless steel or copper) or ceramic. The zeolite solid catalyst is generally coated on the substrate mechanically such as by dip coating or plasma arc. A binder and surfactant may also be used to a provide better adherence of the zeolite solid catalyst to the substrate.
The electrodes may be positioned in the gas flow downstream of a baghouse. The D.C. voltage applied between the electrodes may be less than 34 volts to be effective to ionize the water vapor as previously described, but be sufficiently low to avoid the presence of hydrogen gas in substantial quantities downstream of the solid catalysts in the stack gas stream as described. The electrodes in the gas flow upstream of the first flow-through solid catalyst insulated from containment of the gas flow may apply such voltage to ionize water vapor in the gas flow and reduce moisture content of the gas flow in the first flow-through solid catalyst to be below 8% or 5% or to provide a lower or different moisture content as desired.
The exhaust stack may be adapted to exit gases from the third flow-through solid catalyst with at least 80% or 90% reduction in carbon oxides, sulfur oxides, and nitrogen oxides compared to the stack gases after reaching the electrodes.
The apparatus in addition may have a venturi positioned in the gas flow downstream of the third flow-through solid catalyst to stabilize gas flow through the solid catalysts. The apparatus may also include stabilizing veins to improve laminar flow of the stack gases through the solid catalysts. Stabilizing veins may improve efficiency of separation of pollutants from the stack gases. Stabilizing veins may be positioned upstream or downstream of the electrodes in the gas stream, but may be more advantageously positioned downstream of the electrodes before the gas stream enters the flow-through solid catalyst.
The blend of natural sodium zeolite and natural calcium zeolite in the second flow-through solid catalyst may be between 25% and 75%.
The first flow-through solid catalyst, the second flow-through solid catalyst, and the third flow-through solid catalyst may also each have a porosity of total surface area not greater than 800 m2/g. Also a fourth flow-through solid catalyst of calcium zeolite may also be provided in the gas flow after passing the pair of electrodes and before the first flow-through solid catalyst with a porosity of total surface area not greater than 1200 m2/g, or not greater than 800 m2/g, adapted to collect bauxite compounds before passage through the first flow-through solid catalyst. The fourth flow-through solid catalyst also may be adapted to be periodically purged with nitrogen. Where a fourth flow-through solid catalyst is provided, exhaust stack gases may exit from the third flow-through solid catalyst with at least 70% or 90% reduction in bauxite compounds, carbon oxides, sulfur oxides, nitrogen oxides, and mercury oxides compared to the stack gases delivered to the pair of electrodes.
The apparatus may comprise at least two series of sequential gas flows both through a pair of electrodes, a first flow-through solid catalyst, a second flow-through solid catalyst, and a third flow-through solid catalyst, provided in parallel, so stack gases can be cleaned through one of the series of solid catalysts while the other series of solid catalysts can be purged.
Also disclosed is a method of drying and cleaning stack gases comprising the steps of:                (a) passing a contained stack gas flow, selected from the group consisting of volatiles from combustion of coal or from combustion of natural gas or from a cement kiln, through a pair of electrodes adapted to be positioned inline in the gas flow and applying a D.C. voltage between the electrodes to reduce moisture content of the gas flow through the flow-through solid catalysts without creating substantial amounts of hydrogen gas;        (b) passing stack gas flow from the electrodes through a first flow-through solid catalyst of calcium zeolite comprising natural zeolite particles of a majority between 44 μm and 64 μm in size at a temperature above the dew point between 125° F. and 500° F. and a pressure between 3 psi and 200 psi adapted to reduce carbon oxides in the stack gas flow;        (c) passing the stack gas flow from the first flow-through solid catalyst through a second flow-through solid catalyst of a blend between 25% and 75% of sodium zeolite and calcium zeolite comprising natural sodium and with the calcium zeolite particles comprised of a majority between 65 μm and 125 μm in size at a temperature above the dew point between 125° F. and 500° F. and a pressure between 3 psi and 200 psi adapted to reduce sulfur oxides in the stack gas flow;        (d) passing the stack gas flow from the second flow-through solid catalyst through a third flow-through solid catalyst of calcium zeolite comprising natural zeolite particles of a majority between 78 μm and 204 μm at a temperature above the dew point between 125° F. and 500° F. and a pressure between 3 psi and 200 psi adapted to reduce nitrogen oxides in the stack gas flow; and        (e) operating the stack gas flow sequentially past the pair of electrodes and through the first solid catalyst, the second solid catalyst, and the third solid catalyst to provide at least 70% reduction in sulfur oxides, nitrogen oxides and carbon oxide in the stack gas flow.        
In the method, the voltage between the electrodes may be below 34 volts, and the gas flow sequentially circulated past the pair of electrodes and through the first flow-through solid catalyst, the second flow-through solid catalyst, and the third flow-through solid catalyst also may remove from the gas flow at least 50% or 70% of mercury in all forms. The pair of electrodes in step (a) may also be positioned in the gas flow downstream of a baghouse. The method of drying and cleaning stack gas may also have the pair of electrodes in the gas flow upstream of the first flow-through solid catalyst insulated from containment of the gas flow with D.C. voltage applied to the electrodes to ionize water vapor in the gas flow and reduce moisture content of the gas flow in the first flow-through solid catalyst, preferably to below 8% or 5% or a lower or different moisture content as desired.
Alternatively, a method of drying and cleaning stack gases is disclosed comprising the steps of:                (a) passing a contained stack gas flow selected from the group consisting of volatiles from combustion of coal or from combustion of natural gas or from a cement kiln by a pair of electrodes positioned inline in the gas flow and applying a D.C. voltage between the electrodes to ionize water vapor in the gas flow without creating substantial amounts of hydrogen gas and reduce moisture content of the gas flow in the flow-through solid catalyst in the gas flow before reaching the pair of electrodes;        (b) passing stack gas flow from the pair of electrodes through a first flow-through solid catalyst comprised of calcium zeolite of natural zeolite particles of a majority between 44 μm and 64 μm in size at a temperature above the dew point between 125° F. and 500° F. and a pressure between 3 psi and 200 psi adapted to reduce carbon oxides in the stack gases;        (c) passing the stack gas flow from the first flow-through solid catalyst through a second flow-through solid catalyst comprised of a blend between 25% and 75% of sodium zeolite and calcium zeolite of natural sodium and calcium zeolite particles of a majority between 65 μm and 125 μm in size at a temperature above the dew point between 125° F. and 500° F. and a pressure between 3 psi and 200 psi adapted to reduce sulfur oxides in the stack gases;        (d) passing the stack gas flow from the second flow-through solid catalyst through a third flow-through solid catalyst comprised of calcium zeolite of natural zeolite particles of a majority between 78 μm and 204 μm at a temperature above the dew point between 125° F. and 500° F. and a pressure between 3 psi and 200 psi adapted to reduce nitrogen oxides in the stack gases and providing a stack gas flow exiting the third solid catalyst with at least 70% reduction in sulfur oxides, nitrogen oxides and carbon oxide; and        (e) optionally periodically purging residuals from the first solid catalyst, the second solid catalyst, and the third solid catalyst by intermittently passing liquid or gaseous nitrogen through the solid catalysts to remove solids and liquids collected from the stack gas flow by the solid catalysts.        
In the alternative method of drying and cleaning stack gas described above, the voltages between the electrodes may be less than 34 volts, and the stack gas may have the flow sequentially circulated past the same or a different pair of electrodes and through one of the parallel series of a first flow-through solid catalyst, a second flow-through solid catalyst, and a third flow-through solid catalyst so that one series of flow-through solid catalysts may be cleaned for use while another series of flow-through solid catalysts is used in cleaning stack gas.
The method also may remove from the gas flow at least 50% of mercury or at least 70% of mercury in all forms.
The electrodes in step (a) of the alternative method of cleaning and drying may be positioned in the gas flow downstream of a baghouse. The alternative method of drying and cleaning stack gas may also have the additional step of passing the gas flow through a venture positioned downstream of the third flow-through solid catalyst to stabilize the gas flow through the solid catalysts.
The alternative method of drying and cleaning stack gas may also comprise a fourth flow-through solid catalyst of calcium zeolite comprising natural zeolite particles between 44 μm and 64 μm in size positioned in the stack gas flow after the pair of electrodes and before the first solid catalyst with an electrical charge on said fourth flow-through solid catalyst to separately collect bauxite compounds from the stack gas flow before passing through the first solid catalyst. In this embodiment, the stack gas exiting a stack from the third solid catalyst may have at least 70% or 90% reduction in bauxite compounds, carbon oxides, sulfur oxides, nitrogen oxides, and mercury oxide compared to the stack gas flow delivered through the stack.
The alternative method of drying and cleaning stack gas may have the pair of electrodes positioned in the gas flow upstream of the first flow-through solid catalyst insulated from containment of the gas flow with applied D.C. voltage to ionize water vapor without creating substantial amounts of hydrogen gas in the gas flow, and reduce moisture content of the gas flow through the flow-through solid catalysts to below, for example, 8% or 5% or a lower or different moisture content as desired.
The alternative method of drying and cleaning stack gas may comprise the additional step of passing the gas flow through a venturi positioned downstream of the third flow-through solid catalyst to stabilize the gas flow flow-through solid catalysts.
The alternative method of drying and cleaning stack gas may have at least two series of stack gas flows are provided in parallel to provide for the gas flow to passed a pair of electrodes inline and through a first solid catalyst, a second solid catalyst, and a third solid catalyst to enable at least one solid catalyst in series of solid catalysts can be purged while the stack gas flow continues to be dried and cleaned through a series of solid catalysts and optionally another pair of electrodes.
A second alternative method of drying and cleaning stack gases is disclosed comprising the steps of:                (a) passing a stack gas flow of less than 7% oxygen selected from the group consisting of volatiles from combustion of coal or from combustion of natural gas or from a cement kiln by a pair of electrodes positioned generally inline in the gas flow and to ionize water vapor without creating substantial amounts of hydrogen gas and reduce moisture content of the gas flow through the flow-through solid catalyst as described below;        (b) passing the gas flow from the pair of electrodes through a first flow-through solid catalyst comprised of calcium zeolite of natural zeolite particles at a temperature above the dew point between 125° F. and 500° F. and a pressure between 3 psi and 200 psi adapted to reduce carbon oxides from the stack gases and increase oxygen levels in the stack gases;        (c) passing the gas flow from the first flow-through solid catalyst through a second flow-through solid catalyst comprised of a blend between 25% and 75% of sodium zeolite and calcium zeolite of natural sodium and calcium zeolite particles at a temperature above the dew point between 125° F. and 500° F. and a pressure between 3 psi and 200 psi adapted to reduce sulfur oxides from the stack gases and increase oxygen levels in the stack gases;        (d) passing the gas flow from the second flow-through solid catalyst through a third flow-through solid catalyst comprised of calcium zeolite of natural zeolite particles at a temperature above the dew point between 125° F. and 500° F. and a pressure between 3 psi and 200 psi adapted to reduce nitrogen oxides in the stack gases and increase oxygen levels in the stack gas and providing gas flow exiting the third flow-through solid catalyst with at least 70% reduction in carbon oxides, sulfur oxides, and nitrogen oxides and providing at least a 15% increase in oxygen content.        
The electrodes in step (a) may be positioned in the gas flow downstream of a baghouse and the voltage between the electrodes may be less than 34 volts. Also the second alternative method of drying and cleaning stack gas may have the pair of electrodes in the gas flow upstream of the first flow-through solid catalyst insulated from containment of the gas flow with an applied voltage to the electrodes to ionize water vapor in the gas flow and reduce moisture content of the gas flow in the first flow-through solid catalyst.
The second alternative method of drying and cleaning stack gas may have the stack gas flow sequentially circulated past the pair of electrodes and through the first flow-through solid catalyst, the second flow-through solid catalyst, and the third flow-through solid catalyst also removes from the gas flow at least 50% or at least 70% of mercury in all forms.
The second alternative method of drying and cleaning stack gas may comprise the additional step of passing the gas flow through a venturi positioned downstream of the third flow-through solid catalyst to stabilize the gas flow through flow-through the solid catalysts.
The second alternative method of drying and cleaning stack gas may comprise in addition a fourth flow-through solid catalyst of calcium zeolite comprising natural zeolite particles between 44 μm and 64 μm in size positioned in the stack gas flow after the pair of electrodes and before the first catalytic solid catalyst with an electrical charge on said fourth flow-through solid catalyst to separately collect bauxite compounds from the stack gas flow before passing through the first solid catalyst. In this alternative method of drying and cleaning stack gas may have the stack gas exiting a stack from the third flow-through solid catalyst may have at least 70% or at least 90% reduction in bauxite compounds, carbon oxides, sulfur oxides, nitrogen oxides, and mercury oxide compared to the stack gas flow delivered through the stack.
The second alternative method of drying and cleaning stack gas may have at least two series of stack gas flows provided in parallel to pass the same or a different pair of electrodes inline to dry the stack gas by applying a voltage between the electrodes to ionize the water vapor without creating substantial amounts of hydrogen gas and through a series of a first flow-through solid catalyst, a second flow-through solid catalyst, and a third flow-through solid catalyst so that one stack gas flow can be dried and cleaned by the method described, while an alternative series of a first flow-through solid catalyst, a second flow-through solid catalyst, and a third flow-through solid catalyst may be purged for reuse.
A third alternative method of drying and cleaning stack gases is disclosed comprising the steps of:                (a) passing a stack gas flow selected from the group consisting of volatiles from combustion of coal or from combustion of natural gas or from a cement kiln by at least two electrodes positioned generally inline in the gas flow and applying a D.C. voltage between the electrodes sufficient to ionize the water vapor in the stack gas flow without creating substantial amounts of hydrogen gas and reduce moisture content of the gas flow through the flow-through solid catalysts described below;        (b) passing the gas flow from the pair of electrodes through a first flow-through solid catalyst comprised of calcium zeolite with a porosity of a total surface area not greater than 1200 m2/g to reduce carbon oxides from the stack gases and increase oxygen levels in the stack gas;        (c) passing the gas flow from the first flow-through solid catalyst through a second flow-through solid catalyst comprised of a blend between 25% and 75% of sodium zeolite and calcium zeolite with a porosity of a total surface area not greater than 1200 m2/g to reduce sulfur oxides from the gas flow and increase oxygen levels in the gas flow;        (d) passing the gas flow from the second flow-through solid catalyst through a third flow-through solid catalyst comprised of calcium zeolite comprising natural zeolite particles with a porosity of a total surface area not greater than 1200 m2/g to reduce nitrogen oxides and providing gas exiting the third solid catalyst with at least 70% reduction in sulfur oxides, nitrogen oxides and carbon oxides and at least a 15% increase in oxygen content.        
The electrodes in step (a) of this third alternative method may be positioned in the gas flow downstream of a baghouse. This third alternative method of drying and cleaning stack gas may also provide the pair of electrodes in the gas flow upstream of the first flow-through solid catalyst and insulated from containment of the gas flow, and may apply D.C. voltage less than 34 volts to ionize water vapor in the gas flow and reduce moisture content of the gas flow in the first flow-through solid catalyst, preferably to below 8% or 5% or a lower or different moisture content as desired.
Note that in the method and alternative methods described above, the first flow-through solid catalyst, the second flow-through solid catalyst, and the third flow-through solid catalyst may include other sizes of particles of zeolite as explained in more detail below.
In the third alternative method of drying and cleaning stack gas, an additional fourth flow-through solid catalyst of calcium zeolite comprising natural zeolite particles with a porosity of a total surface area not greater than 1200 m2/g may be positioned in the stack gas flow after the pair of electrodes and before the first flow-through solid catalyst with an electrical charge to separately collect bauxite compounds from the stack gas flow before passing through the flow-through first solid catalyst. This method of drying and cleaning stack gas may have the stack gas exiting a stack from the third flow-through solid catalyst with at least 70% or at least 90% reduction in bauxite compounds, carbon oxides, sulfur oxides, nitrogen oxides, and mercury oxide compared to the stack gas flow delivered to the stack.
This third alternative method of drying and cleaning stack may have at least two series of stack gas flows provided in parallel to pass the same or a different pair of electrodes positioned inline to ionize the water vapor in the stack gas without creating substantial amounts of hydrogen gas and through a series first flow-through solid catalyst, a second flow-through solid catalyst, and a third flow-through solid catalyst so that one solid catalyst of stack gas flow can be dried and cleaned by the method described while another series of flow-through solid catalysts are purged for use.
This third alternative method of drying and cleaning stack gas may also comprise in addition a fourth catalytic flow-through solid catalyst comprised of calcium zeolite of natural zeolite particles between 44 μm and 64 μm in size positioned in the stack gas flow after the pair of electrodes and before the first flow-through solid catalyst, with an electrical charge on said fourth catalytic flow-through solid catalyst, to separately collect bauxite compounds from the stack gas flow before passing through the first flow-through solid catalyst. In this alternative method of drying and cleaning stack gas, the stack gas exiting a stack from the third flow-through solid catalyst has at least 70% or at least 90% reduction in bauxite compounds, sulfur oxides, nitrogen oxides, mercury oxide, and carbon oxides compared to the stack gas flow delivered through the stack to the electrode.
The method and alternative methods of drying and cleaning stack gas may comprise the additional step of passing the gas flow through a venturi positioned downstream of the third flow-through solid catalyst to stabilize the gas flow through the flow-through solid catalysts.
The method and alternative methods of drying and cleaning stack gas may have the stack gas flow sequentially circulated past the pair of electrodes and through the first flow-through solid catalyst, the second flow-through solid catalyst, and the third flow-through solid catalyst to also remove at least 50% or at least 70% of mercury in all forms from the gas flow.
Also disclosed is a fertilizer product produced by the steps of:                (a) passing a stack gas flow selected from the group consisting of volatiles from combustion of coal or from combustion of natural gas or from a cement kiln by a pair of electrodes positioned generally inline in the gas flow with D.C. voltage applied between the electrodes to ionize water vapor, without creating substantial amounts of hydrogen gas, and reduce moisture content of the gas flow below, for example, 8% or 5% of moisture content in the gas flow;        (b) passing the gas flow from the pair of electrode through a first flow-through solid catalyst comprised of calcium zeolite of natural zeolite particles of a majority between 44 μm and 64 μm in size, at a temperature above the dew point between 125° F. and 500° F. and a pressure between 3 psi and 200 psi, adapted to reduce carbon oxides in the stack gases;        (c) passing the gas flow from the first flow-through solid catalyst through a second flow-through solid catalyst comprised of a blend between 25% and 75% of sodium zeolite and calcium zeolite of natural sodium and calcium zeolite particles of a majority between 65 μm and 125 μm in size, at a temperature above the dew point between 125° F. and 500° F. and a pressure between 3 psi and 200 psi, adapted to reduce sulfur oxides in the stack gas flow;        (d) passing the gas flow from the second flow-through solid catalyst through a third flow-through solid catalyst comprised of calcium zeolite of natural zeolite particles of a majority between 78 μm and 204 μm, at a temperature above the dew point between 125° F. and 500° F. and a pressure between 3 psi and 200 psi, to reduce nitrogen oxides in the stack gas flow and providing gas exiting the third solid catalyst with at least 70% reduction in carbon oxides, sulfur oxides, and nitrogen oxides; and        (e) optionally periodically purging residuals from the first flow-through solid catalyst, the second flow-through solid catalyst, and the third flow-through solid catalyst by intermittently passing nitrogen through the solid catalysts to remove residuals collected from the stack gases by the solid catalysts.        
Also disclosed is fertilizer product produced by the steps of:                (a) passing a stack gas flow of less than 7% oxygen selected from the group consisting of volatiles from combustion of coal or from combustion of natural gas or from a cement kiln by a pair of electrodes adapted to be positioned generally inline in the gas flow with a voltage applied to the electrodes to ionize water vapor in the gas flow without creating substantial amounts of hydrogen gas and reduce moisture content of the gas flow, for example, below at least 8%;        (b) passing the gas flow from the electrodes through a first flow-through solid catalyst comprised of calcium zeolite of natural zeolite particles at a temperature above the dew point between 125° F. and 500° F. and a pressure between 3 psi and 200 psi adapted to reduce carbon oxides from the stack gases and increase oxygen levels in the stack gas;        (c) passing the gas flow from the first flow-through solid catalyst through a second flow-through solid catalyst comprised of a blend between 25% and 75% of sodium zeolite and calcium zeolite of natural sodium and calcium zeolite particles of at a temperature above the dew point between 125° F. and 500° F. and a pressure between 3 psi and 200 psi adapted to reduce sulfur oxides from the stack gases and increase oxygen levels in the stack gas;        (d) passing the gas flow from the second flow-through solid catalyst through a third flow-through solid catalyst comprised of calcium zeolite of natural zeolite particles at a temperature above the dew point between 125° F. and 500° F. and a pressure between 3 psi and 200 psi adapted to reduce nitrogen oxides in the stack gases and increase oxygen levels in the stack gas flow; and providing gas flow exiting the third flow-through solid catalyst with at least 70% reduction in sulfur oxides, nitrogen oxides and carbon oxides and at least a 15% increase in oxygen content.        
Also disclosed is fertilizer product produced by the steps of:                (a) passing a stack gas flow from the group consisting of volatiles from combustion of coal or from combustion of natural gas or from a cement kiln by a pair of electrodes positioned generally inline in the gas flow and applying a D.C. voltage to ionize water vapor without creating substantial amounts of hydrogen gas and reduce moisture content of the gas flow through the flow-through solid catalysts;        (b) passing the gas flow from the pair of electrodes though a first flow-through solid catalyst comprised of natural calcium zeolite with a porosity of a total surface area of not greater than 1200 m2/g adapted to reduce carbon oxides in the stack gas;        (c) passing the gas flow from the first flow-through solid catalyst through a second flow-through solid catalyst comprised of a blend of natural sodium zeolite and natural calcium zeolite with a porosity of a total surface area of not greater than 1200 m2/g adapted to reduce sulfur oxides in the stack gas with the blend of sodium zeolite and calcium zeolite between 25% and 75%;        (d) passing the gas flow from second flow-through solid catalyst through third flow-through solid catalyst comprised of natural calcium zeolite with a porosity of a total surface area not greater than 1200 m2/g adapted to reduce nitrogen oxides in the stack gas and providing gas exiting the third flow-through solid catalyst with at least 70% reduction in sulfur oxides, nitrogen oxides, and carbon oxides; and        (e) purging residuals collected from the first flow-through solid catalyst, the second flow-through solid catalyst, and the third flow-through solid catalyst and collecting said residuals purged from the first solid catalyst, the second solid catalyst, and the third solid catalyst to provide a fertilizer product.        
Also disclosed is a method of reducing moisture content in a gas flow comprising the steps of:                (a) positioning generally inline a pair of electrodes in a gas flow with moisture content to be reduced to ionize water vapor in the gas flow without creating substantial amounts of hydrogen gas;        (b) providing insulating containment of the gas flow, such as a pipe, from the electrodes; and        (c) applying voltage between the electrodes to ionize water vapor in the gas flow to reduce moisture content of the gas flow to at least 8% without creating substantial amounts of hydrogen gas.        
In the various embodiments of the method, apparatus or fertilizer product, carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxide (NOx), sulfur dioxide (SO2) and nitrogen dioxide (NO2) in the gas stack flow is reduced. The solid waste may also include nitrate salt formed by reaction of nitrogen and nitrogen compounds retained in the zeolite solid catalysts with available oxygen. Exit from the third flow-through solid catalyst may typically include excess oxygen from the reduction according in the first, second and third flow-through solid catalysts as described above. The apparatus may also include a product purged with liquid nitrogen.
In any case, the exiting stack gas with increased oxygen levels may be returned from the gas cleaning system to the burner where it is combusted with the coal or natural gas. The system may also include a solid waste draw for collecting the materials and drawing the waste material away from the gas cleaning section.
Other details, objects and advantages of the present invention will become apparent from the description of the preferred embodiments described below in reference to the accompanying drawings.